A known propelling unit for an omni directional vehicle comprises a main wheel including an annular member and a plurality of drive rollers arranged circumferentially along the annular member so as to be rotatable around the tangential axial line thereof at the corresponding position, a pair of drive disks disposed on either lateral side of the main wheel so as to be rotatable around the respective central axial lines and drive rollers mounted on each drive disk so as to be rotatable around an axial line which is in a skewed relationship to the central axial line of the drive disk and engaging the outer circumferential surface of the corresponding driven roller at the outer circumferential surface thereof. See Patent document 1, for instance.
This friction drive device is used as a propulsion unit of an inverted pendulum type vehicle constructed as a unicycle. The two drive disks are rotatably supported by the frame of the inverted pendulum type vehicle, and rotatably support the main wheel by interposing the driven rollers with the left and right sets of the drive rollers from either side.
In the inverted pendulum type vehicle incorporated with this friction drive device, the drive rollers are pushed against the driven rollers so that the rotation of the drive disks is transmitted to the driven rollers via the drive rollers owing to the frictional engagement between the drive rollers and the driven rollers. When the two drive disks are rotatively actuated in the same direction at the same speed, the main wheel rotates around the central axial line thereof. When the drive disks are rotatively actuated in different directions or at different speeds, the driven rollers rotate around the respective central axial lines (around the tangential axial line of the annular member) while the main wheel rotates around the central axial line thereof, or the driven rollers rotate around the respective central axial lines while the main wheel remains stationary. At any event, the vehicle is able to travel in the fore and aft, lateral and oblique directions while maintaining an upright posture by the inverted pendulum control.